Which description correctly defines the heat-affected zone?

• A. The Weld Metal.
• B. The Filler Metal.
• C. The Heat-Affected Zone.
• D. The Weld Root.

Answer: (C)

When metal is welded, heat travels into the surrounding base metal. The heat-affected zone is the portion of that base metal that is heated enough to change its microstructure and properties but does not melt. This zone sits between the fully melted weld metal and the untouched base metal, and its characteristics (like hardness and grain size) depend on the heat input and cooling rate. The weld metal describes the material that actually melts and solidifies to form the weld, while the filler metal is additional material that may be melted to fill gaps. The weld root refers to the deepest point of penetration in the joint. Therefore, the description that correctly defines the heat-affected zone is the base metal region whose microstructure has been altered by heat without melting.